pub fn main() {
    println!("{}", 20);
    println!("{}", "Hello, world!");
    println!("{0} {1}", 1, 2);
    println!("{a} {b} {c} ", a = 1, b = "2", c = 3.14);

    println!("{:b} 二进制展示", 22);

    //左边对齐，右边填充空格，总共占位6个字符
    println!("{number:>width$}", number = 1, width = 6);

    //左边对齐，右边填充0，总共占位6个字符
    println!("{number:>0width$}", number = 1, width = 6);


}
